Atrial fibrillation remains the most commonly occurring cardiac arrhythmia. It is associated with a lower quality of life and a higher rate of morbidity & mortality. Cryotherapy and radiofrequency catheter ablations for the purpose of eliminating atrial fibrillation have become a mainstream treatment option. They produce lesions that block the spread of electrical activity from the sites of abnormal activity, including the pulmonary veins. Today, there are limited means for real-time monitoring of tissue injury during cardiac ablation procedures. To address this need, we studied the fluorescence of endogenous NADH as a live marker of tissue injury during the ablation procedure and have confirmed the feasibility of this approach in blood perfused animal hearts. STTR Phase I support will provide us with the necessary funds to accelerate the project into its next phase. Studies will be conducted in small and large, fully-anesthetized open-chest animals. The goals of Aim1 are to compare the effectiveness of laser vs LED based illumination, sensitivity and spatial resolution of internal vs external cameras, and to test the shape and material for the inflatable balloons and to fit all the components within lumen of a 12Fr (4mm) diameter catheter. In Aim 2 several iterations of catheters designed by LuxCath will be brought to the GWU Institute of Surgical Endoscopy (WISE) surgical suite for testing. Images of NADH fluorescence will be acquired in real time to visualize gaps of viable tissue between ablation lesions at various clinically relevan sites, including the pulmonary veins. Electrical activity recordings will be linked to NADH images to correlate ablation gaps to the occurrence of post-ablation reentries. The immediate goal of Phase I is to develop a pre-clinical stand-alone visualization catheter that can be used during AF ablation procedures to evaluate the cardiac lesions around the ostia of the pulmonary veins. Ultimately, a new generation of stand- alone visualization catheters as well as ablation catheters incorporating visualization capabilities will be developed thus enabling real-time visualization of ablated tissue at the time of ablation or using the same device to perform the ablations. Such new imaging technologies will pave the way for easier, faster, safer, more cost-effective, and more reliable minimally invasive AF ablation procedures..